Patients with a clinico-neuroradiological mismatch pattern shown on the magnetic resonance imaging/Computed Tomography in the acute phase of stroke are more likely to benefit from reperfusion, are suitable candidates for endovascular therapy, and have a better clinical prognosis.

The ASTER Trial showed similar results between stent-retrievers and contact aspiration concerning the recanalization grade in anterior circulation occlusions. However, we still observe late and futile recanalizations, secondary either to extended ischemic lesions at baseline, long-time procedures or intraprocedural complications. The First Pass Effect that is the complete/nearly complete recanalization after the first maneuver, independently on the technique used, has been strongly associated with better clinical outcomes . In a recent paper we proposed a novel approach to identify those cases that could be treated with a specific technique (stent-retriever) with higher chances to achieve a complete or nearly complete recanalization, with lower procedure times and lower complication rates. This approach is focused on the identification of a regular or irregular phenotype of the occlusion site in patients with an M1-Middle Cerebral Artery occlusion. The phenotype is defined as "regular" whether the profile of the occlusion is abruptly cut without any irregularity and as "irregular" if any irregularity of the profile of the occlusion is observed. One of the hypotheses that could explain these results could be related to the composition of the clot : a soft and less organized clot could be more easily flattened by the pulsatile flow and therefore determine a regular aspect of the occlusion. A more solid and organized clot would, on the contrary, maintain an irregular profile because it would not be flattened by the blood flow and the contrast medium could highlight the irregularities of the proximal face of the clot.

The latter could be a favorable target for the use of a stent-retriever since the interaction between a solid clot and the struts of the stent could increase the chance to retrieve the clot. Therefore, we propose this randomized controlled trial to assess the superiority of stent-retrievers compared to contact aspiration in the treatment of irregular phenotype occlusions of the M1-Middle Cerebral Artery.

Statistical analyses will be independently performed by the Biostatistics Department of University of Lille under the responsibility of Julien Labreuche. Data will be analyzed using the SAS software (SAS Institute Inc, Cary, NC, USA). A detailed statistical analysis plan will be written and finalized prior to the database lock. Baseline characteristics will be described for each group. Quantitative variables will be expressed as mean (standard deviation) or median (interquartile range) for non-Gaussian distribution. Qualitative variables will be expressed as frequencies and percentages. Normality of distribution will be assessed graphically and using the Shapiro-Wilk test. All applicable statistical tests will be 2-sided and no correction for multiple comparisons will be applied; all secondary objectives will be considered as exploratory and results were reported with only effect size estimates with their confidence intervals (CIs). All CIs presented will be 95%CI and 2-sided. The final report will be written, based on the CONSORT statement recommendations.

Inclusion Criteria:

• Age ≥ 18 years
• M1-Middle Cerebral Artery occlusion
• Eligible for mechanical thrombectomy: groin puncture performed within 24 hours from the first symptoms or from the last time the patient was seen normal.
• Presence of a mismatch on Magnetic resonance imaging MRI or CT (computed tomography) scan
• Baseline mRS <2
• Irregular occlusion phenotype on the first angiographic run
• Informed consent obtained from the patients/his proxy or following an emergency procedure
• Being covered by a national health insurance

Exclusion Criteria:

• Isolated M2 occlusions
• Clinical history, past imaging or clinical judgment suggesting underlying intracranial stenosis
• Severe contrast medium allergy or absolute contraindication to use of iodinated products
• Patients with severe or fatal comorbidities that will likely prevent improvement or follow-up, or that will render the procedure unlikely to benefit the patient
• Angiographic evidence of carotid dissection or tandem cervical occlusion or stenosis requiring treatment
• Pregnancy (urine or serum beta HCG test for women of child-bearing potential)
• Patient benefiting from a legal protection (guardianship or curatorship)
• Being deprived of liberty

The angiographic outcomes will be assessed by a centralized Core Laboratory, not involved in patient management.